The present invention relates to the so-called Signaling ATM Adaptation Layer (SAAL) which is defined in the ITU-T Q.2100. In the following, the main function of the SAAL and the layers related thereto are described in short.
FIG. 1 illustrates the placement of the SAAL in broadband signalling stacks (protocol stacks) for User-Network-Interface (UNI) and Network-Node-Interface (NNI) operations. For the UNI, Q.2931 (ITU-T specification, Q.2931 is a variation of ISDN layer 3 Q.931) is used to set up and tear down a connection. It operates over the Signalling ATM Adaptation Layer (SAAL) which is designed especially for Q.2931. These layers operate over the conventional ATM (Asynchronous Transfer Mode) layer and a selected physical layer (indicated by PHY in FIG. 1). For the NNI, the broadband ISUP (B-ISDN) and Message Transfer Part 3 (MTP3) are variations of their counterparts in the SS7 signalling standard. The SAAL supports their operations. These layers also operate over the conventional ATM layer and a selected physical layer.
The SAAL serves to provide a correct transfer of signalling data on a broadband signalling link. It relieves the user of concerning about data errors, duplicates, or insertions that may occur on the signalling link.
SAAL provides a link monitoring service, and checks whether links are stable and error-free enough to be used. It can also take a link out of service if it becomes unreliable. SAAL also provides for flow control procedures and employs a mechanism to insure that two exchanges do not create congestion problems.
The SAAL comprises two protocol entities, a Service Specific Coordination Function (SSCF) and a Service Specific Connection Oriented Protocol (SSCOP) which contribute to the overall functions of the SAAL. These overall operations are coordinated by a Layer Management (LM).
The SSCF maps primitives received from the MTP3 layer to the required SSCOP signals and vice versa. That is, it transfers signals the SSCOP and the MTP 3 or Q.2931 layer. Moreover, SSCF is responsible for the flow control. That is, it notifies the user about levels of congestion in order to prevent a cell loss. It also regulates its flow of Protocol Data Units (PDUs) to the lower layers to prevent congestion at the other end. Furthermore, SSCF is responsible for the link status. Based on primitives it receives from MTP3 and SSCOP, the SSCF maintains information (local state variables) about the status of the link, such as information indicating that the link is aligned ready or that it is out of service and so on. Using this information, it may generate primitives/signals to MTP3 and SSCOP to aid in managing the link. In addition, the SSCF reports to the Layer Management (LM) when a link is released. It relies upon LM to help in the error monitoring function. Finally, SSCF maintains the information (state variables) about all the alignment procedures that are taking place when a link is brought into service or taken out of service.
On the other hand, the SSCOP performs sequencing and acknowledgement of traffic, for example. That is, keeps all signalling units (messages) that flow across the link in sequential order, and it also provides for retransmission of defective traffic. To make certain the exchanges (communication nodes) are operational, each node executes a so-called “keep alive” procedure with its neighbour exchange. SSCOP also contains a procedure that allows the local user to look at the SSCOP queue for purposes of determining the status of messages. The SSCOP also provides a number of status reporting operations.
The SSCOP interacts with a further sublayer, the so-called Common Part AAL Protocol (CP-AAL) or AAL5CP (ATM Adaptation Layer type 5 Common Part). The CP-AAL performs further AAL functions not contained in the SSCF and SSCOP layers.
The Layer Management (LM), which is defined in ITU-T Q.2144, interacts with the layers to perform a variety of operations, administration and maintenance (OAM) functions. LM determines if a signalling link should be taken out of service or put into service (the latter function is called link proving). As part of these operations, links are monitored for excessive delays in the delivery of traffic. LM also permits a certain number of errors to occur on the link in order to avoid unnecessary changeovers to alternate links. Furthermore, a number of ongoing measurements are taken by the LM. For example, counters are maintained on how long each link has been in service, how often it has failed, how often and how many times the link has experienced congestion, and other information.
The Layer Management is originally described only for the SAAL at NNI, and, as described above, the main function of it is the error monitoring and quality measurement production of NNI SAAL.
Upon initialisation of a signalling link/channel using SAAL, for each of the above-described sublayers resources have to be provided. That is, when a signalling link/channel using SAAL is configured in the network element, dedicated SAAL resources have to be provided. The SAAL resources comprise an SSCOP resource, an SSCF resource and a CP-AAL (AAL5CP) resource.
The provision and management of resources are in particular important in case the SAAL stack is implemented in a distributed implementation environment.
However, according to the prior art such a provision is not described.